I know the previous version of Unity did not work with Blender 2.5. I havent had a chance to try Unity 3 with Blender 2.5. Does it work?
http://answers.unity3d.com/questions/21608/blender-2-5x-importation/21653#21653
http://answers.unity3d.com/questions/22291/importing-from-blender
NO, it seems that Unity3 will NOT import blender 2.5x files at this time. Though, if you uncheck cameras on an FBX export from blender 2.5x, you CAN then import the FBX into Unity, just not the native ".blend" files yet.
There appears to be an official Blender 2.5 Support thread with a plugin for Unity (which I haven’t tested) that makes the import as clean as with 2.49.
I had problem with importing textured mesh. I tried to make a simple geometry Blender 2.5, then I export to FBX and load in Unity - all was ok. Then I applied a texture on mesh, exported to FBX and loaded in Unity 3 - Unity wasnt able to find a mesh. I dont know, where is the problem.
This post on BlenderArtists describes how to get Blender 2.5 working with Unity 3.x
try exporting as an autodesk 3ds file.
Unity wont import 2.59 files yet. Exporting as FBX does work.
Unity will import 2.49 files.
Also:
If both are installed you cant import from 2.49, and 2.59 wont unwrap meshes for skinning.
Yes Unity 3.0 should take blender files. If you are having problems dragging Blender files in to unity then try this Link :)